Doped titanium dioxide

ABSTRACT

Pyrogenically prepared titanium dioxide doped by means of an aerosol contains an oxide from the group zinc oxide, platinum oxide, magnesium oxide and/or aluminum oxide as the doping component.  
     It is prepared as follows: in the pyrogenic preparation of titanium dioxide, a metal salt solution is atomized to form an aerosol and injected into the production stream.  
     The titanium dioxide may be used as a photocatalyst or as a UV adsorber.

[0001] This application claims priority from European Application No. 00106 612.5, filed on Mar. 28, 2000, and European Application No. 00 106687.7, filed on Mar. 29, 2000, the subject matter of each of which ishereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to doped titanium dioxide, to a process forits preparation and to its use.

[0004] 2. Background Information

[0005] Pyrogenic titanium dioxide (obtainable commercially as DegussaTiO2 P 25) is distinguished by the variety of its possible uses in thefield of photocatalysis.

[0006] (R. W. Matthews, S. R. McEvoy, J. Photochem. Photobiol.A: Chem.,64 (1992) 231-246.

[0007] R. I. Bickley et al., Journal of Solid State Chemistry, 92(1991), 178-190.

[0008] R. Franke, C. Franke, Chemosphere, Vol. 39, No. 15 (1999),2651-2659.

[0009] H. Zen, JETI (1998), 46 (10), 66-67.

[0010] It is used as a reference material having a high degree ofphotocatalytic activity.

[0011] (V. Loddo et al., Applied Catalysis B: Environmental 20 (1999) ,29-45).

SUMMARY OF THE INVENTION

[0012] The invention provides a titanium dioxide doped by means of anaerosol and containing an oxide from the group zinc oxide, platinumoxide, magnesium oxide and/or aluminium oxide as the doping component.

[0013] The invention also provides a process for the preparation of thetitanium dioxide doped by means of an aerosol, which process ischaracterised in that an aerosol is fed into a flame such as is used forthe preparation of pyrogenic titanium dioxide by means of flamehydrolysis, that aerosol is mixed homogeneously before or during thereaction with the gas mixture of the flame oxidation or flamehydrolysis, the aerosol/gas mixture is allowed to react in a flame, andthe resulting doped, pyrogenically prepared oxide is separated from thegas stream in a known manner, there being used as the starting materialfor the aerosol a salt solution or suspension containing the componentof the substance to be doped, which may be a metal salt or metalloidsalt or mixtures of the two or a suspension of an insoluble metal ormetalloid compound or a mixture of the two, the aerosol being producedby atomisation by means of a two-component nozzle or by an aerosolgenerator, preferably by ultrasonic atomisation.

[0014] There may be used as the substance to be doped salts of zinc,magnesium, aluminium and/or noble metals such as platinum, palladium,silver, gold. There may preferably be used aqueous solutions of thosesalts, which may optionally be acidified. There may preferably be usedas salts zinc chloride, hexachloroplatinic acid, magnesium chloride,aluminium chloride.

[0015] The process for doping by means of an aerosol may be carried outsubstantially as described in the document EP 0 850 876 A1.

[0016] The process of flame hydrolysis to prepare pyrogenic titaniumdioxide is known from Ullmann's Enzyklopädie der technischen Chemie, 4thedition, Volume 21, page 464.

[0017] The titanium dioxides doped by means of an aerosol according tothe invention may exhibit concentrations of the doping substances in arange of from 0.00001 to 20 wt. %., preferably from 0.1 to 10,000 ppm.The BET surface areas may be from 5 to 150 m²/g, preferably from 35 to110 m²/g.

[0018] In order to produce a high level of photocatalytic activity, theBET surface area may be from 65 to 80 m²/g. In that case, the amount ofdoping component may be from 40 to 800 ppm.

[0019] In order to produce low photocatalytic activity, the BET surfacearea may be from 35 to 60 m²/g. In that case, the amount of dopingcomponent may be greater than 1000 ppm.

[0020] When the titanium dioxides doped by means of an aerosol accordingto the invention have a high level of photocatalytic activity, they maybe used for the purification of waste air.

[0021] They may be fixed to a support.

[0022] When the titanium dioxides according to the invention have a highlevel of photocatalytic activity, they may be used for the degradationof impurities in waste water and/or waste air. In that case, thetitanium dioxides may be used both suspended in the waste water and/orwaste air and fixed to a support.

[0023] When the titanium dioxides according to the invention have lowphotocatalytic activity, they may be used as an adsorbent for UVradiation. They may be used in the coating of glasses or in plastics.

[0024] The titanium dioxides according to the invention may also be usedfor application to glasses, to plastics, for the removal of impuritiesfrom air, water, etc. when they have a high level of photocatalyticactivity.

[0025] The titanium dioxides according to the invention having a highlevel of photocatalytic activity may also be used for the sterilisationof water with UV irradiation.

[0026] The photocatalytic activity of the titanium dioxides doped bymeans of an aerosol according to the invention is tested in thephotocatalytic degradation of chlorinated hydrocarbons with UVirradiation in optionally acidified, aqueous suspension.

[0027] In those tests, it is found that the photocatalytic activity ofthe titanium dioxides according to the invention in optionally acidifiedaqueous suspension can be increased or reduced by doping with oxides ofmetals/noble metals or metalloids.

[0028] Surprisingly, the photocatalytic activity in the degradation ofchlorinated hydrocarbons in aqueous suspension is increased even thoughhomogeneous intermixing of the doping component and the titanium dioxidehas taken place. The doping component in that case is therefore notexclusively on the titanium dioxide, but also in the titanium dioxide.

[0029] A higher degree of doping contributes towards lowering thephotocatalytic activity. In order to determine the photocatalyticactivity, the degradation of chlorinated hydrocarbons (4-chlorophenol(4-CP) and dichloroacetic acid (DCA)) with UV irradiation in a stirredreactor is tested.

[0030] In order to increase the rate of photocatalytic degradation ofchlorinated hydrocarbons in optionally acidic aqueous suspension by thedoped pyrogenically prepared titanium dioxides, the BET surface area ispreferably in the range of from 70 to 85 m²/g.

[0031] In order to lower the photocatalytic activity, which is likewisetested by the degradation of 4-chlorophenol and dichloroacetic acid withUV irradiation in purely aqueous or acidified aqueous suspension, theBET surface area is preferably in the range of from 50 to 60 m²/g.

[0032] Moreover, a change in the amount of doping component leads to achange in the rate of photocatalytic degradation of the chlorinatedhydrocarbons with UV irradiation.

DETAILED DESCRIPTION OF THE INVENTION Examples

[0033] The initial reaction rates (after the first 30 minutes) ofselected doped titanium dioxide catalysts [mg TOC* l-1 min-1 (TOC=totalorganic carbon=organically bonded carbon)] of DCA (dichloroacetic acid)and 4-CP (4-chlorophenol) in an optionally acidified aqueous suspensionwith UW irradiation are measured.

[0034] The photocatalytic rate of degradation of chlorinatedhydrocarbons with UV irradiation in optionally acidified aqueoussuspension with the use of pure titanium dioxide Degussa P 25 asphotocatalyst is used as the reference value (zero value). The durationof the tests with Degussa P 25 is not more than 360 minutes. The initialreaction rate of the photocatalytic degradation of chlorinatedhydrocarbons in optionally acidified aqueous suspension is determined.

[0035] The photocatalytic degradation of chlorinated hydrocarbons withUV irradiation in purely aqueous or acidified aqueous suspension, thatis to say without the addition of titanium dioxide, over several hours(max. 360 minutes=min.) is likewise monitored.

[0036] The results of the initial reaction rate and the results inrespect of the photocatalytic degradation of chlorinated hydrocarbons inpurely aqueous or acidified suspension are given in Table 3, Table 4 andTable 5.

[0037] Doping with Al₂O₃, PtO₂ or MgO gives an especially high initialreaction rate of the degradation of dichloroacetic acid and4-chlorophenol (initial concentration of both chlorinated hydrocarbons:c=120 mg/l) in purely aqueous or acidified aqueous suspension with UVirradiation, in comparison with Degussa P 25 (see Table 5).

[0038] If ZnO is used as the doping substance, different effects areachieved according to the BET surface area and the doping amount.

[0039] With a BET surface area of 78 m²/g and a ZnO doping amount of430±20 ppm, the initial reaction rate of the degradation ofdichloroacetic acid and 4-chlorophenol in purely aqueous or acidifiedaqueous suspension with UV irradiation is greatly increased incomparison with Degussa P 25.

[0040] With a BET surface area of 56 m²/g and a ZnO doping amount of0.13 (±0.02) %, the initial reaction rate in the degradation ofdichloroacetic acid in purely aqueous or acidified aqueous suspensionwith UW irradiation is increased by only 29% as compared with Degussa P25.

[0041] In the degradation of 4-chlorophenol, the initial reaction ratein purely aqueous or acidified aqueous suspension with UV irradiation isreduced by 31% in comparison with Degussa P 25 (see Table 5).

[0042] In addition, pure TiO₂ having a BET surface area of 82 m²/g isalso tested as a photocatalyst, in order to rule out the possibilitythat the increase in the initial reaction rate of the photocatalyticdegradation of 4-chlorophenol and dichloroacetic acid in purely aqueousor acidified aqueous suspension with UV irradiation, in comparison withDegussa titanium dioxide P 25, is based solely on the increase insurface area.

[0043] Although the increase in surface area does bring about increasedphotocatalytic degradation of 4-chlorophenol and dichloroacetic acid,the increase is not as great as that brought about by doping (see Table5).

[0044] Preparation of the Doped Titanium Dioxides

[0045] The burner arrangement used in Examples 1 to 6 is showndiagrammatically in FIG. 1.

[0046] According to FIG.1, the core element of the apparatus is the openburner (1) of known type, as is customarily used for the preparation ofpyrogenic oxides. The burner (1) consists of an inner nozzle (3), fromwhich the main gas stream flows into the flame tube (2) and burns. Theinner nozzle (3) is surrounded by a further nozzle (4) (jacket nozzle),from which ring or secondary hydrogen flows in is order to avoid caking.Between the nozzle outlet and the flame tube there is arranged adiaphragm (5) through which the aerosol is fed in, the aerosol gasstream from the diaphragm being mixed homogeneously with the gas streamof the inner nozzle and the jacket nozzle. The aerosol is produced in anaerosol generator (6) (ultrasonic atomiser). The starting material usedfor the aerosol is an aqueous salt solution containing the metal/noblemetal or metalloid to be doped as a salt or chloro acid in dissolved ordispersed/suspended form.

[0047] The aerosol produced by the aerosol generator (6) is guided bymeans of a carrier gas stream through the heating zone (7), in which thewater evaporates and there remain behind in the gas phase small saltcrystallites in finely divided form.

[0048] The individual conditions for the preparation of the oxides aregiven in Table 1.

Example 1 Doping with Al₂O₃

[0049] 0.66 kg/h of TiCl₄ is vaporised at 280° C. and introduced intothe central pipe of the burner. 0.54 Nm³/h of hydrogen and 3.41 Nm³/h ofair are additionally fed into the central pipe. The gas mixture flowsfrom the inner nozzle of the burner and burns, since it is an openburner, into the flame tube. 0.23 Nm³/h of jacket or secondary hydrogenis fed into the jacket nozzle, which surrounds the central nozzle, inorder to prevent caking at the nozzles.

[0050] The aerosol is applied from the diaphragm (diameter: 35 mm; slotwidth: 0.4 mm), which is located in a horizontal position between theoutlet from the burner head and the flame tube. The aerosol is analuminium chloride salt aerosol, which is produced by ultrasonicatomisation of a is 1% aqueous AlCl₃×6H₂O solution in the aerosolgenerator in an amount of 126 g/h. The aluminium salt aerosol is guidedwith the aid of the carrier gas, which is 0.04 Nm³/h of nitrogen,through a heated pipe, the aerosol changing at temperatures of about215° C. into a gas and a salt crystal aerosol.

[0051] The reaction gases, additional air from the surroundings drawn inthrough the open burner and the Al₂O₃-doped, pyrogenically preparedtitanium dioxide that has formed, are drawn through the cooling systemby means of low pressure and thereby cooled to 100-160° C. The solid isseparated from the gas stream by means of a filter or cyclone. Theresulting Al₂O₃-doped, pyrogenically prepared titanium dioxide is afinely divided white powder.

[0052] In a subsequent step, the hydrochloric acid residues adhering tothe titanium dioxide are removed at elevated temperature by treatmentwith air containing water vapour. The BET surface area of the doped,pyrogenically prepared titanium dioxide is 75 m²/g. Further analyticaldata are given in Table 2.

Example 2 Doping with PtO₂

[0053] 0.65 kg/h of TiCl₄ is vaporised at 280° C. and introduced intothe central pipe of the burner. 0.54 Nm³/h of hydrogen and 3.41 Nm³/h ofair are additionally fed into the central pipe. The gas mixture flowsfrom the inner nozzle of the burner and burns, since it is an openburner, into the flame tube. 0.23 Nm³/h of jacket or secondary hydrogenis fed into the jacket nozzle, which surrounds the central nozzle, inorder to prevent caking at the nozzles.

[0054] The aerosol is applied from the diaphragm (diameter: 35 mm; slotwidth: 0.4 mm), which is located in a horizontal position between theoutlet from the burner head and the flame tube. The aerosol is ahexachloroplatinic acid aerosol, which is produced by ultrasonicatomisation of a 0.5% aqueous H₂PtCl₆ solution in the aerosol generatorin an amount of 27.0 g/h. The hexachloroplatinic acid aerosol is guidedwith the aid of the carrier gas, which is 0.04 Nm³/h of nitrogen,through a heated pipe, the aerosol changing at temperatures of about344° C. into a gas and a salt crystal aerosol.

[0055] The reaction gases, additional air from the surroundings drawn inthrough the open burner and the PtO₂-doped, pyrogenically preparedtitanium dioxide that has formed, are drawn through a cooling system bymeans of low pressure and thereby cooled to 100-160° C. The solid isseparated from the gas stream by means of a filter or cyclone. Theresulting PtO₂-doped, pyrogenically prepared titanium dioxide is afinely divided white powder.

[0056] In a subsequent step, the hydrochloric acid residues adhering tothe titanium dioxide are removed at elevated temperature by treatmentwith air containing water vapour. The BET surface area of thePtO₂-doped, pyrogenically prepared titanium dioxide is 73 m²/g. Furtheranalytical data are summarised in Table 2.

Example 3 Doping with MgO

[0057] 0.66 kg/h of TiCl₄ is vaporised at 280° C. and introduced intothe central pipe of the burner. 0.54 Nm³/h of hydrogen and 3.41 Nm³/h ofair are additionally fed into the central pipe. The gas mixture flowsfrom the inner nozzle of the burner and burns, since it is an openburner, into the flame tube. 0.23 Nm³/h of jacket or secondary hydrogenis fed into the jacket nozzle, which surrounds the central nozzle, inorder to prevent caking at the nozzles.

[0058] The aerosol is applied from the diaphragm (diameter: 35 mm; slotwidth: 0.4 mm), which is located in a horizontal position between theoutlet from the burner head and the flame tube. The aerosol is amagnesium chloride salt aerosol, which is produced by ultrasonicatomisation of a 0.5% aqueous MgCl₂×6H₂O solution in the aerosolgenerator in an amount of 21.4 g/h. The magnesium salt aerosol is guidedwith the aid of the carrier gas, which is 0.04 Nm³/h of nitrogen,through a heated pipe, the aerosol changing at temperatures of about331° C. into a gas and a salt crystal aerosol.

[0059] The reaction gases, additional air from the surroundings drawn inthrough the open burner and the MgO-doped, pyrogenically preparedtitanium dioxide that has formed, are drawn through a cooling system bymeans of low pressure and thereby cooled to 100-160° C. The solid isseparated from the gas stream by means of a filter or cyclone. TheMgO-doped, pyrogenically prepared titanium dioxide is a finely dividedwhite powder.

[0060] In a subsequent step, the hydrochloric acid residues adhering tothe titanium dioxide are removed at elevated temperature by treatmentwith air containing water vapour. The BET surface area of the MgO-doped,pyrogenically prepared titanium dioxide is 77 m²/g. Further analyticaldata are summarised in Table 2.

Example 4 Doping with ZnO

[0061] 0.65 kg/h of TiCl₄ is vaporised at 280° C. and introduced intothe central pipe of the burner. 0.54 Nm³/h of hydrogen and 3.41 Nm³/h ofair are additionally fed into the central pipe. The gas mixture flowsfrom the inner nozzle of the burner and burns, since it is an openburner, into the flame tube. 0.23 Nm³/h of jacket or secondary hydrogenis fed into the jacket nozzle, which surrounds the central nozzle, inorder to prevent caking at the nozzles.

[0062] The aerosol is applied from the diaphragm (diameter: 35 mm; slotwidth: 0.4 mm), which is located in a horizontal position between theoutlet from the burner head and the flame tube. The aerosol is a zincchloride salt aerosol, which is produced by ultrasonic atomisation of a3% aqueous ZnCl₂ solution in the aerosol generator in an amount of 31.7g/h. The zinc salt aerosol is guided with the aid of the carrier gas,which is 0.04 Nm³/h of nitrogen, through a heated pipe, the aerosolchanging at temperatures of about 303° C. into a gas and a salt crystalaerosol.

[0063] The reaction gases, additional air from the surroundings drawn inthrough the open burner and the ZnO-doped, pyrogenically preparedtitanium dioxide that has formed, are drawn through a cooling system bymeans of low pressure and thereby cooled to 100-160° C. The solid isseparated from the gas stream by means of a filter or cyclone. Theresulting ZnO-doped, pyrogenically prepared titanium dioxide is a finelydivided white powder.

[0064] In a subsequent step, the hydrochloric acid residues adhering tothe titanium dioxide are removed at elevated temperature by treatmentwith air containing water vapour. The BET surface area of the ZnO-doped,pyrogenically prepared titanium dioxide is 78 m²/g. Further analyticaldata are summarised in Table 2.

Example 5 Doping with ZnO

[0065] 1.32 kg/h of TiCl₄ are vaporised at 280° C. and introduced intothe central pipe of the burner. 0.33 Nm³/h of hydrogen and 2.68 Nm³/h ofair are additionally fed into the central pipe. The gas mixture flowsfrom the inner nozzle of the burner and burns, since it is an openburner, into the flame tube. 0.1 Nm³/h of jacket or secondary hydrogenis fed into the jacket nozzle, which surrounds the central nozzle, inorder to prevent caking at the nozzles.

[0066] The aerosol is applied from the diaphragm (diameter: 35 mm; slotwidth: 0.4 mm), which is located in a horizontal position between theoutlet from the burner head and the flame tube. The aerosol is a zincchloride salt aerosol, which is produced by ultrasonic atomisation of a2% aqueous ZnCl₂ solution in the aerosol generator in an amount of 112.6g/h. The zinc salt aerosol is guided with the aid of the carrier gas,which is 0.04 Nm³/h of nitrogen, through a heated pipe, the aerosolchanging at temperatures of about 215° C. into a gas and a salt crystalaerosol.

[0067] The reaction gases, additional air from the surroundings drawn inthrough the open burner and the ZnO-doped, pyrogenically preparedtitanium dioxide that has formed, are drawn through the cooling systemby means of low pressure and thereby cooled to 100-160° C. The solid isseparated from the gas stream by means of a filter or cyclone. TheZnO-doped, pyrogenically prepared titanium dioxide is a finely dividedwhite powder.

[0068] In a subsequent step, the hydrochloric acid residues adhering tothe titanium dioxide are removed at elevated temperature by treatmentwith air containing water vapour. The BET surface area of the ZnO-doped,pyrogenically prepared titanium dioxide is 56 m²/g. Further analyticaldata are summarised in Table 2.

Example 6 Preparation of TiO₂

[0069] 0.42 kg/h of TiCl₄ is vaporised at 280° C. and introduced intothe central pipe of the burner. 0.21 Nm³/h of hydrogen, 3.78 Nm³/h ofair and 0.04 Nm³/h of nitrogen are additionally fed into the centralpipe. The gas mixture flows from the inner nozzle of the burner andburns, since it is an open burner, into the flame tube. 0.23 Nm³/h ofjacket or secondary hydrogen is fed into the jacket nozzle, whichsurrounds the central nozzle, in order to prevent caking at the nozzles.

[0070] The reaction gases, additional air from the surroundings drawn inthrough the open burner and the pyrogenically prepared titanium dioxidethat has formed, are drawn through a cooling system by means of lowpressure and thereby cooled to 100-160° C. The solid is separated fromthe gas stream by means of a filter or cyclone. The pyrogenicallyprepared titanium dioxide having a large surface area is a finelydivided white powder.

[0071] In a subsequent step, the hydrochloric acid residues adhering tothe titanium dioxide are removed at elevated temperature by treatmentwith air containing water vapour. The BET surface area of thepyrogenically prepared titanium dioxide is 82 m²/g. Further analyticaldata are summarised in Table 2.

[0072] Experimental procedure for determining the rate of photocatalyticdegradation of chlorinated hydrocarbons in suspension.

[0073] The total running time of the tests to investigate the rate ofphotocatalytic degradation of chlorinated hydrocarbons such as4-chlorophenol (4-CP) and dichloroacetic acid (DCA) with UV irradiationin purely aqueous or acidified aqueous suspension is not more than 360minutes.

[0074] The degradation reaction is carried out in a stirred reactor. Inaddition, the suspension to be studied is pumped from the storagecontainer to the stirred reactor and back, so that uniform UVirradiation is ensured. The pH value of the suspension is in the rangeof from 4 to 7, preferably at pH=5. The temperature in the stirredreactor is in the range of from 25 to 40° C., preferably from 30 to 35°C. The concentration of the particular photocatalytically active or lessactive titanium dioxide, that is to say pure titanium dioxide P 25 oraccording to Example 6, Tables 3 and 4 or doped titanium dioxide asdescribed in Tables 3-4, is 1 g/l. The temperature is kept constantwithin the mentioned range by means of continuous pumping from thestorage vessel to the UV irradiation unit and back, as well as bycooling of the UV lamp system by means of cooling water. The progress ofthe degradation of the chlorinated hydrocarbons with UV irradiation ismonitored continuously throughout the degradation reaction.

[0075] From this determination of the TOC value (TOC=total organiccarbon=organically bonded carbon) which takes place at regularintervals, it is possible to determine the factor TOC/TOC₀ (TOC₀=initialconcentration of organically bonded carbon in suspension). TOC/TOC₀indicates the percentage TOC content at a particular withdrawal time.

[0076] The progress of the degradation of chlorinated hydrocarbons isplotted in a TOC/TOC₀-time curve. The rate of degradation of Degussa P25 is tested as the standard, likewise under the same conditions.

[0077] The entire course of the curve is recorded.

[0078] Blind tests of the degradation of 4-chlorophenol anddichloroacetic acid with UV irradiation but without the addition oftitanium dioxides are also carried out.

[0079] If titanium dioxide is not used, the TOC/TOC₀ values stillpresent are greater than 89%, so that virtually no degradation takesplace in that case.

[0080] Test results of the photocatalytic degradation of 4-chlorophenol.

Example 7 Blind Test

[0081] Only 4-chlorophenol in acidified aqueous solution is introducedinto the storage vessel and the stirred reactor and treated. No TiO₂ isadded. A TOC/TOC₀-time curve is recorded. After 300 minutes, 89.82% ofthe initial TOC content is still present. An initial reaction rate isnot determined.

Example 8 P 25

[0082] 4-Chlorophenol and 1 g/l of titanium dioxide P 25 in acidifiedaqueous suspension are introduced into the storage vessel and thestirred reactor and treated as indicated above. A TOC/TOC₀-time curve isrecorded. After 300 minutes, only 20.91% of the initial TOC content isstill present. The initial reaction rate is used as the standard andtaken as zero. All values obtained with the titanium dioxides accordingto Examples 9 to 14 are based on this P 25 value.

Example 9 Doping with Al₂O₃

[0083] 4-Chlorophenol and 1 g/l of catalyst according to Example 1 inacidified aqueous suspension are introduced into the storage vessel andthe stirred reactor and treated as indicated above. A TOC/TOC₀-timecurve is recorded. After 300 minutes, only 8.36% of the initial TOCcontent of the 4-chlorophenol is still present. The initial reactionrate is increased by 51% in comparison with P 25 (Example 8).

Example 10 Doping with PtO₂

[0084] 4-Chlorophenol and 1 g/l of catalyst according to Example 2 inacidified aqueous suspension are introduced into the storage vessel andthe stirred reactor and treated as indicated above. A TOC/TOC₀-timecurve is recorded. After 300 minutes, only 17.73% of the initial TOCcontent of the 4-chlorophenol is still present. The initial reactionrate is increased by 26% in comparison with P 25 (Example 8).

Example 11 Doping with MgO

[0085] 4-Chlorophenol and 1 g/l of catalyst according to Example 3 inacidified aqueous suspension are introduced into the storage vessel andthe stirred reactor and treated as indicated above. A TOC/TOC₀-timecurve is recorded. After 300 minutes, only 10.91% of the initial TOCcontent of the 4-chlorophenol is still present. The initial reactionrate is increased by 36% in comparison with P 25 according to Example 8.

Example 12 Doping with ZnO

[0086] 4-Chlorophenol and 1 g/l of catalyst according to Example 4 inacidified aqueous suspension are introduced into the storage vessel andthe stirred reactor and treated as indicated above. A TOC/TOC₀-timecurve is recorded. After 300 minutes, only 9.55% of the initial TOCcontent of the 4-chlorophenol is still present. The initial reactionrate is increased by 36% in comparison with P 25 according to Example 8.

Example 13 Doping with ZnO

[0087] 4-Chlorophenol and 1 g/l of catalyst according to Example 5 inacidified aqueous suspension are introduced into the storage vessel andthe stirred reactor and treated as indicated above. A TOC/TOC₀-timecurve is recorded. After 300 minutes, 37.65% of the initial TOC contentof the 4-chlorophenol is still present. The initial reaction rate islowered by 31% in comparison with P 25 according to Example 8.

Example 14 TiO₂

[0088] 4-Chlorophenol and 1 g/l of catalyst according to Example 6 inacidified aqueous suspension are introduced into the storage vessel andthe stirred reactor and treated as indicated above. A TOC/TOC₀-timecurve is recorded. After 300 minutes, only 18.18% of the initial TOCcontent of the 4-chlorophenol is still present. The initial reactionrate is increased by 12% in comparison with P 25 according to Example 8.

[0089] Test results of the photocatalytic degradation of dichloroaceticacid (DCA).

Example 15 Blind Test

[0090] Only dichloroacetic acid in acidified aqueous solution isintroduced into the storage vessel and the stirred reactor and treatedas indicated above. No TiO₂ is added. A TOC/TOC₀-time curve is recorded.After 245 minutes, 95.45% of the initial TOC content is still present.An initial reaction rate is not determined.

Example 16 P 25

[0091] Dichloroacetic acid and 1 g/l of titanium dioxide P 25 inacidified aqueous suspension are introduced into the storage vessel andthe stirred reactor and treated as indicated above. A TOC/TOC₀-timecurve is recorded. After 245 minutes, 0% of the initial TOC content ispresent. The initial reaction rate is used as the standard and taken aszero. All values obtained with the titanium dioxides according toExamples 17 to 22 are based on this P 25 value.

Example 17 Doping with Al₂O₃

[0092] Dichloroacetic acid and 1 g/l of catalyst according to Example 1in acidified aqueous suspension are introduced into the storage vesseland the stirred reactor and treated as indicated above. A TOC/TOC₀-timecurve is recorded. After 201.89 minutes, 0% of the initial TOC contentof the dichloroacetic acid was present. The initial reaction rate isincreased by 84% in comparison with P 25 according to Example 16.

Example 18 Doping with PtO₂

[0093] Dichloroacetic acid and 1 g/l of catalyst according to Example 2in acidified aqueous suspension are introduced into the storage vesseland the stirred reactor and treated as indicated above. A TOC/TOC₀-timecurve is recorded. After 206.76 minutes, 0% of the initial TOC contentof the dichloroacetic acid is present. The initial reaction rate isincreased by 80% in comparison with P 25 according to Example 16.

Example 19 Doping with MgO

[0094] Dichloroacetic acid and 1 g/l of catalyst 3 in acidified aqueoussuspension are introduced into the storage vessel and the stirredreactor and treated as indicated above. A TOC/TOC₀-time curve isrecorded. After 200.27 minutes, 0% of the initial TOC content of thedichloroacetic acid is present. The initial reaction rate is increasedby 73% in comparison with P 25 according to Example 16.

Example 20 Doping with ZnO

[0095] Dichloroacetic acid and 1 g/l of catalyst according to Example 4in acidified aqueous suspension are introduced into the storage vesseland the stirred reactor and treated as indicated above. A TOC/TOC₀-timecurve is recorded. After 189.73 minutes, 0% of the initial TOC contentof the dichloroacetic acid is present. The initial reaction rate isincreased by 76% in comparison with P 25 according to Example 16.

Example 21 Doping with ZnO

[0096] Dichloroacetic acid and 1 g/l of catalyst according to Example 5in acidified aqueous suspension are introduced into the storage vesseland the stirred reactor and treated as indicated above. After 245minutes, a residual TOC/TOC₀value of 14.54% is present. After 245minutes, complete degradation of the dichloroacetic acid is not to beobserved. The initial reaction rate is increased by only 29% incomparison with P 25 according to Example 16.

Example 22 TiO₂

[0097] Dichloroacetic acid and 1 g/l of catalyst according to Example 6in acidified aqueous suspension are introduced into the storage vesseland the stirred reactor and treated as indicated above. A TOC/TOC₀-timecurve is recorded. After 206.76 minutes, 0% of the initial TOC contentof the dichloroacetic acid is present. The initial reaction rate isincreased by 55% in comparison with P 25 according to Example 16. TABLE1 Experimental conditions in the preparation of the oxides Exam- PrimarySec. Gas Amount of N₂ BET surface ple TiCl₄ air air H₂ core H₂ jacket N₂core temp. aerosol aerosol area No. [kg/h] [Nm³/h] [Nm³/h] [Nm³/h][Nm³/h] [Nm³/h] [° C.] Salt solution [g/h] [Nm³/h] [m²/g] 1 0.66 3.41 00.54 0.23 0 235 1% AlCl₃ × 6H₂O 126.0 0.04 75 2 0.65 3.41 0 0.54 0.23 0240 0.5% H₂PtCl₆ 27.0 0.04 73 3 0.66 3.41 0 0.54 0.23 0 240 0.5% MgCl₂ ×6H₂O 21.4 0.04 77 4 0.65 3.41 0 0.54 0.23 0 235 3% ZnCl₂ 31.7 0.04 78 51.32 2.68 0 0.33 0.10 0 247 2% ZnCl₂ 112.6 0.04 56 6 0.42 3.78 0 0.210.23 0.04 230 no doping 0 82

[0098] Explanation:

[0099] Primary air=amount of air in the central pipe; Sec. air=secondaryair; H₂ core=hydrogen in the central pipe; H₂ jacket=jacket hydrogen; N₂core=nitrogen in the central pipe; Gas temp.=gas temperature in thenozzle of the central pipe; Amount of aerosol=mass flow rate of the saltsolution converted into aerosol form; N₂ aerosol=amount of carrier gas(nitrogen) in the aerosol TABLE 2 Analytical data of the oxides obtainedaccording to Examples 1 to 6 BET Amount of Exam- surface doping Cl LD LIpH Tamped ple area comp. content [wt. [wt. [4% density No. [m²/g] [ppm][ppm] %] %] sus.] [g/l] 1 75 606 130  0.55 1.26 5.09 209 2 73  93 530.63 1.75 4.96 241 3 77  48 57 1.3 0.85 5.79 220 4 78 415 44 0.77 1.266.05 219 5 56 1270  1320  1.01 1.23 4.93 315 6 82 / 0.84 1.79 5.01 152

[0100] Explanation:

[0101] Doping components (see Table 4) in μg/g (ppm); LD=loss on drying(2 h at 105° C.), in accordance with DIN/ISO 787/II, ASTM D 280, JIS K5101/21); LI=loss on ignition (2 h at 1000° C.); in accordance with DIN55921, ASTM D 1208, JIS K 5101/23, based on the substance dried at 105°C.; tamped density in accordance with DIN/ISO 787/IX, JIS K 5101/18 (notsieved). TABLE 3 Test results of the photocatalytic degradation of 4-CP(4- chlorophenol) by means of titanium dioxide and doped titaniumdioxides after 300 minutes (min.). Residual TOC/TOC₀ at t = 300 min.Example Catalyst [%] 7 Blind test with 89.82 irradiation (without TiO₂)8 P25 20.91 9 1. TiO2/Al2O3 8.36 10 2. TiO2/PtO2 17.73 11 3. TiO2/MgO10.91 12 4. TiO2/ZnO 9.55 13 5. TiO2/ZnO 37.65 14 6. TiO2 18.18

[0102] TABLE 4 Test results of the photocatalytic degradation of DCA(dichloroacetic acid) by means of titanium dioxide or doped titaniumdioxides Residual TOC/TOC₀ Time Example Catalyst [%] [min.] 15 Blindtest with 95.45 245 irradiation (without TiO2) 16 P25 0 245 17 1.TiO2/Al2O3 0 201.89 18 2. TiO2/PtO2 0 206.76 19 3. TiO2/MgO 0 200.27 204. TiO2/ZnO 0 189.73 21 5. TiO2/ZnO 14.54 245 22 6. TiO2 0 206.76

[0103] TABLE 5 Initial reaction rates of the titanium dioxides DCA 4-CPincrease in % increase in % Doping component/ BET surface (comp. with(comp. with Catalyst amount area [m²/g] P 25 P 25 P25 / 50 0 0 acc. toExample 1. TiO₂/Al₂O₃ Al₂O₃/606 ppm 75 84 51 acc. to Example 2.TiO₂/PtO₂ PtO₂/93 ppm 73 80 26 acc. to Example 3. TiO₂/MgO MgO/48 ppm 7773 36 acc. to Example 4. TiO₂/ZnO ZnO/415 ppm 78 76 36 acc. to Example5. TiO₂/ZnO ZnO/0.127% 56 29 — 31 (reduction) acc. to Example 6. TiO₂ /82 55 12

[0104] Reactor volume: 1.7 l

[0105] Source of radiation: UVH1022 Z4 iron-doped high-pressuremercury-discharge lamp;

[0106] Exclusion power 500 W (Heraeus) Catalyst concentration: 1 g/l

[0107] Initial concentration of the chlorinated hydrocarbons: 120 mg/l

[0108] The tests to determine the initial reaction rates of thephotocatalytic degradation of chlorinated hydrocarbons with UVirradiation and using titanium dioxides and doped titanium dioxidesprepared by flame hydrolysis are carried out in purely aqueous oracidified aqueous suspension. The suspension is stirred constantly andirradiated continuously with the iron-doped high-pressuremercury-discharge lamp UVH1022 Z4. Cooling is provided for the lamp inorder to ensure constant conditions. Likewise, the suspension is kept ata constant temperature by continuous pumping from the storage containerto the reactor and back and by cooling.

What is claimed is:
 1. Pyrogenically prepared titanium dioxide doped bymeans of an aerosol and containing an oxide from the group zinc oxide,platinum oxide, magnesium oxide and/or aluminium oxide as the dopingcomponent.
 2. Process for the preparation of the pyrogenically preparedtitanium dioxide doped by means of an aerosol according to claim 1,wherein an aerosol is fed into a flame such as is used for thepreparation of pyrogenic titanium dioxide by means of flame hydrolysis,that aerosol is mixed homogeneously before or during the reaction withthe gas mixture of the flame oxidation or flame hydrolysis, theaerosol/gas mixture is allowed to react in a flame, and the resultingdoped pyrogenically prepared oxide is separated from the gas stream in aknown manner, there being used as the starting material for the aerosola salt solution or suspension containing the component of the substanceto be doped, which may be a metal salt or metalloid salt or mixtures ofthe two or a suspension of an insoluble metal or metalloid compound or amixture of the two, the aerosol being produced by atomisation by meansof a two-component nozzle or by an aerosol generator, preferably byultrasonic atomisation.
 3. A photocatalyst comprising the pyrogenicallyprepared titanium dioxide doped by means of an aerosol according toclaim
 1. 4. An adsorbant for UV radiation comprising the pyrogenicallyprepared titanium dioxide doped by means of an aerosol according toclaim
 1. 5. A process for purification of waste water comprisingcontacting the pyrogenically prepared titanium dioxide doped by means ofan aerosol according to claim 1 with said waste water.
 6. A process forpurification of waste air and/or waste gasses comprising contacting thepyrogenically prepared titanium dioxide doped by means of an aerosolaccording to claim 1 with said waste air and/or waste gases.